The present invention relates to rare earth oxysulfide particulate materials, and particularly relates to terbium-activated gadolinium oxysulfide phosphors exhibiting an enhanced green:blue emission ratio as well as a method for producing such enhancement.
Rare earth oxysulfides have long been recognized in the art as valuable luminescent materials. These phosphors are in the form of a solid solution having a matrix of the rare earth oxysulfide compound with a small amount of an activator or dopant dispersed throughout the matrix. The activator normally is also a rare earth element.
Among such rare earth activated rare earth oxysulfides is the blue-green emitting terbium-activated rare earth oxysulfide having the nominal formula: EQU Gd.sub.2-x O.sub.2 S:xTb (1)
where x is 0.001 to 0.2. The phosphor is useful, e.g., in the field of x-ray intensifier screens. However, the spectral sensitivity of the x-ray film does not always precisely match the phosphor emission. Thus, it would be desirable to have the capability to adjust the green:blue emission ratio of the phosphor emission to tailor the phosphor emission to the spectral sensitivity of the x-ray film.
Accordingly, it is an object of the present invention to provide a terbium-activated gadolinium oxysulfide phosphor which overcomes the disadvantages of the prior art.
It is another object of the invention to provide a terbium-activated gadolinium oxysulfide phosphor in which the green:blue emission ratio of the phosphor emission is enhanced by the addition of silicon without the presence of fluorine in the phosphor matrix.
It is yet another object of the invention to provide a terbium-activated gadolinium oxysulfide phosphor in which the phosphor emission can be tailored to match to the spectral sensitivity of a particular x-ray film.
It is still another object of the invention to provide a method of enhancing the green:blue emission ratio of a terbium-activated gadolinium oxysulfide phosphor by adding silicon to the phosphor matrix without the presence of fluorine.